The present invention relates to a root pass bead welding method.
Conventionally, one method of adjoining two members and welding them from one side using a dike bead member involves, as shown in FIG. 7, the steps of temporarily welding a dike bead member 30 to a first base member 10, placing a second base member 20 in contact with the dike bead member 30 and forming a cavity 40 between the two base members, and welding the base members from the side defining the cavity. Such a method is disclosed, for example, in Japanese Patent Laid-Open Application No. 70466-1984 and Japanese Patent Laid-Open Application No. 92167-1984, respectively. However, with this conventional welding method a large stress concentration occurs at the welded portion when loads act repeatedly, and cracking a or b occurs at the welded portion, starting from the crack origin A or B. Moreover, it is also difficult to achieve a reliable connection because of residual slits caused by the presence of the dike bead member 30. And there is a certain amount of trouble involved because it is necessary to achieve a certain degree of accuracy in the positioning of the dike bead member 30 on the first base member 10.
On the other hand, penetration beam welding methods that do not use any dike bead member whatsoever can achieve an excellent connection and exhibit excellent fatigue stress and other characteristics since there are no cutouts on the side of the root surface. However, the formation of a favorable root pass bead requires a high level of processing accuracy, and strict management of the welding conditions and assembly accuracy.